What donor vehicle to get disc brakes setup from for 72 swinger.
x2 on the above. the swap hinges on spindle-- that's where the magic happens and everything is available new now. it used to be you needed to get the 73~76 upper with the larger ball joint, but now there's an adapter for the smaller joint to the spindle.
the cost of the consumables new or reman from the parts store negates any savings you'd see in snagging the rotors and calipers unless they're mint.
the biggest issue is finding the stuff used. it's just not out there anymore littering the yard like it once was. the pieces come up quite frequently in the classifieds here, but shipping can sometimes sour a deal.